How mobile phones work

Recreational, toy and amateur radio walkie talkies
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Mobile phones are a little like walkie-talkies. A walkie-talkie uses radio waves to transmit sound from one handset to another, pretty much the way the first mobile phones (radiophones) did.

However, mobile phones are much more complex and versatile than walkie-talkies.

Duplexity

One major difference between walkie-talkies and mobile phones is that walkie-talkies are half-duplex devices while mobile phones are full-duplex.

A half-duplex device uses a single radio frequency. A frequency is like a path which sound takes to travel from one place to another. Because walkie-talkies use the same frequency to talk and listen, only one person can talk at a time.

Full-duplex devices use separate frequencies for talking and listening. That way, both people can talk – and interrupt each other – at once!

Channels challenge

Another big difference is the number of channels between a walkie-talkie and a mobile phone. A frequency is a single path that sound can travel along. A channel consists of a number of frequencies that together form a “highway” for sending and receiving more information.

Most walkie-talkies use just one channel. A typical mobile phone, however, uses thousands of channels!

It’s in the range

Walkie-talkies are point-to-point devices, sending messages directly from one walkie-talkie handset to another. This means that they can only work within a certain distance from one another.

Some walkie-talkies are more powerful than others, but a typical walkie-talkie can transmit about 1.6 km using a 0.25-watt transmitter. To get greater range on a walkie-talkie the handset needs a larger, heavier and clumsier battery.

This makes them useful for builders at construction sites, for instance, because everyone stays within a short distance of each another and can therefore communicate while remaining in range.

Mobile phones send signals to radio towers which are positioned at regular intervals. The area surrounding a tower is known as a cell.

Each radio tower is connected to another and the rest of the telephone network using cables. As someone with a mobile phone moves from cell to cell, their handset automatically reconnects with the radio tower in that cell, so the phone call stays uninterrupted.

This means that calls from mobile phones can be made to virtually any other telephone in the planet. The mobile phone itself simply has to have the power to reach the nearest radio tower.